The present invention relates to block copolymers for directed self-assembly applications, and more specifically to high-chi (χ) block copolymers comprising a surface active fluorinated linking group joining the polymer blocks.
Block copolymers (BCPs) find many applications in solution, bulk and thin films. Thin film applications of BCPs are particularly attractive for nanolithography and patterning due to the ability of some BCPs to form periodic self-assembled structures ranging in feature size from 5 nm to 50 nm. The thin-film self-assembly property of BCPs can be utilized with existing photolithographic techniques to provide a unique approach to long range order for semiconductor applications. This approach, called directed self-assembly (DSA) of block copolymers, promises to extend the patterning capabilities of conventional lithography.
BCPs for directed self-assembly (DSA) applications comprise two or three polymer blocks that can phase segregate into domains characterized by ordered nanoscopic arrays of spheres, cylinders, gyroids, and lamellae. The ability of a BCP to phase segregate depends on the Flory Huggins interaction parameter chi (χ). Poly(styrene)-block-poly(methyl methacrylate), abbreviated as PS-b-PMMA, is the most widely used block copolymer for DSA. However, the minimum half-pitch of PS-b-PMMA is limited to about 10 nm because of lower interaction and interaction parameter (χ) between the PS and PMMA blocks. To enable further feature miniaturization, a block copolymer with higher interaction parameter between two blocks (higher chi) is highly desirable.
For lithography applications, orientation of the block copolymer domains perpendicular to the substrate is typically desired. For PS-b-PMMA this is achieved by coating and thermally annealing the block copolymer layer, which is disposed on an underlayer of non-preferential or neutral material. The underlayer can be grafted to or crosslinked with the underlying substrate layer. Due to a larger difference in the interaction parameter between the domains of higher-χ block copolymers, it is important to control both BCP-air and BCP-substrate interactions. Many orientation control strategies for generating perpendicularly oriented BCP domains have been implemented using higher-χ BCPs. For example, solvent vapor annealing has been used for orientation control of poly(styrene)-b-poly(ethylene oxide) (PS-b-PEO), poly(styrene)-b-poly(dimethylsiloxane) (PS-b-PDMS), poly(styrene)-b-poly(2-vinyl pyridine) (PS-b-P2VP), poly(lactide)-b-poly(4-trimethylsilylstyrene) (PLA-b-PTMSS) and poly(alpha-methylstyrene)-b-poly(4-hydroxystyrene) (PαMS-b-PHOST). Introducing a solvent vapor chamber and kinetics of solvent vapor annealing may complicate DSA processing. Alternatively, a combination of non-preferential wetting underlayer and topcoat has been used with PS-b-P2VP, PS-b-PTMSS and PLA-b-PTMSS block copolymers to achieve perpendicular orientation of the polymer domains during annealing. However, the additional topcoat materials may increase the process cost and complexity.
A need exists for high-χ block copolymers whose topcoat-free thin films self-assemble using thermal annealing to form perpendicularly oriented domain structures on preferential and non-preferential underlayers.